Using the navball at launch?

[Buckeye1]

Is there a rule of thumb for getting a rocket out of Kerbin's atmosphere? All that I've gathered thus far is that powerful rockets can get into space at shallower angles. Alternatively, a rocket solely designed for Kerbin orbit requires about a 45 degree angle when it's all said and done. Since target assist is not an option from launch, how do I know from rocket to rocket what the angle should be? Also, does career mode build off of the tutorials, or am I better off playing around in sandbox first?

[Snark]

20 minutes ago, Buckeye1 said:

Is there a rule of thumb for getting a rocket out of Kerbin's atmosphere?

Plenty.   

The magic phrase you're looking for is "gravity turn"-- try searching Gameplay Questions for that phrase and you'll get lots of discussion.

Here are some useful rules of thumb (bearing in mind that different players have different techniques, so advice may vary somewhat):

1. Design your rocket to have a "reasonable" TWR on the launchpad.  Depending on design and ship size, this may be anywhere from 1.3 to 1.7; I try to keep my life simple by religiously sticking to 1.5.  YMMV.
2. Give your rocket a very gentle eastward nudge practically right off the launch pad, say when you get up to 20 m/s or so.
3. Follow prograde to orbit.

That's basically it.  The tricky bit is deciding just how much of a nudge to give it in step #2.  It's really sensitive; easy to do it too much or too little.  Just how much of a nudge you need will typically depend on your TWR, which is why I like to always have the same launchpad TWR to make it easy for me.  You'll get the nudge amount wrong, a lot.  "Revert to launch" is your friend.  Just try it again and again until you get a feel for it-- practice makes it a lot easier.

Here's how to tell, fairly early on, if you've nailed it:  by the time you reach 10 km altitude, your ship should be canted over about 45 degrees from the vertical, and going well over 300 m/s.

If it's a lot more vertical than 45 degrees at 10 km, you didn't give it enough of a nudge-- revert to launch and try again with a bigger nudge.  If it's a lot more horizontal than 45 degrees at 10 km, you gave it too much of a nudge; revert and try again with a more gentle touch.

 

[Buckeye1]

1 hour ago, Snark said:

 

1. Design your rocket to have a "reasonable" TWR on the launchpad.  Depending on design and ship size, this may be anywhere from 1.3 to 1.7; I try to keep my life simple by religiously sticking to 1.5.  YMMV.

Is the thrust-to-weight ratio displayed in-game? I thought I read somewhere that it's a mod on pc? I'm playing on console, so I only have the stock game. I'm sure I can still figure it out if not.

Edited July 31, 2016 by Buckeye1

[Shadowmage]

25 minutes ago, Buckeye1 said:

Is the thrust-to-weight ratio displayed in-game? I thought I read somewhere that it's a mod on pc? I'm playing on console, so I only have the stock game. I'm sure I can still figure it out if not.

Sadly, it is not displayed anywhere in the stock UI; you have to manually calculate it given the engines' atmospheric thrust and the launch-mass of your rocket.

200kn = 20tons @ 1.0 TWR; in other words you need 10kn per ton of craft for a 1.0 TWR, or around 13kn/ton for a 1.3 TWR.

[Snark]

1 hour ago, Buckeye1 said:

Is the thrust-to-weight ratio displayed in-game? I thought I read somewhere that it's a mod on pc? I'm playing on console, so I only have the stock game. I'm sure I can still figure it out if not.

Not displayed in-game, but trivial to calculate.  Add up all the thrust of your engines, in kN; divide by your total ship mass, in tons; then divide by 9.81 m/s² (Kerbin gravity).  There's your answer.

I usually take off from the pad on SRBs alone, so I actually go about it the other way around:  I start with my desired TWR of 1.5, then use the formula to figure out what percentage to set my SRBs at to give me that.  For example:  Let's say I have a small rocket massing 10 tons on the launch pad, which is taking off using a single Hammer SRB.  So:  10 tons, times 9.81 m/s², times my desired launchpad TWR of 1.5, gives me 147 kN of needed thrust.  The atmospheric thrust of a Hammer is 198 kN, so to get my desired TWR, I set its thrust limiter to 147 / 198 = 74.5%.

[bewing]

An alternate rule of thumb:

There is very little that's interesting about LKO. You really don't ever want to go there unless you have to. There is free fuel on the Mun (if you have the tech). There is even freer fuel on Minmus. There are lots and lots of science points on both. There are many contracts to fill on both. There are satellite contracts to fill in High Kerbin Orbit. None of these things require going to LKO first. Putting a reasonable number of SRBs on your rocket will almost always put you way above the TWR limits that make gravity turns convenient. SRBs are much cheaper than liquid boosters for about the same oomph. SRBs have no gimballing, so they are much harder to steer. A gravity turn is very efficient -- but all it does is get you to LKO. (It is true that once you are in LKO, if you have to go there, it's pretty efficient to go anywhere else from there.)

So, putting all that together, and if you care about money -- another perfectly valid option is to just launch your rockets straight up to the Mun or Minmus. You have to aim, and time it well, and have a more powerful booster stage (you want to be going at least 1600 m/s before you switch to your upper stage) -- but it saves almost 50% on your travel time, and maybe 30% on the cost of your rocket, and it works with much more noodley rockets that would crash if you try to gravity turn them.

There are plenty of things that have to end up in LKO, of course. It's not like you will never go there. So this rule of thumb only applies when you have a choice.

-- And as far as sandbox goes: I kinda think it's always beneficial to have one of each going at the same time. The career mode game gives you odd targets to strive for, that you might never consider in sandbox mode. Once you have something you want to accomplish that you've never done before, you switch to the sandbox mode game and try 80 different ways to see if you can accomplish it. Or you need to design a ship to do a task, and you need to figure out how much fuel and how to steer and all the other design aspects of it -- so you try a dozen different designs in sandbox mode, and launch them, and see what they can do. Which also is very helpful when you forget stuff -- like landing legs or solar panels or antennas or science devices or ....

 

[Buckeye1]

41 minutes ago, bewing said:

An alternate rule of thumb:

There is very little that's interesting about LKO. You really don't ever want to go there unless you have to. There is free fuel on the Mun (if you have the tech). There is even freer fuel on Minmus. There are lots and lots of science points on both. There are many contracts to fill on both. There are satellite contracts to fill in High Kerbin Orbit. None of these things require going to LKO first. Putting a reasonable number of SRBs on your rocket will almost always put you way above the TWR limits that make gravity turns convenient. SRBs are much cheaper than liquid boosters for about the same oomph. SRBs have no gimballing, so they are much harder to steer. A gravity turn is very efficient -- but all it does is get you to LKO. (It is true that once you are in LKO, if you have to go there, it's pretty efficient to go anywhere else from there.)

So, putting all that together, and if you care about money -- another perfectly valid option is to just launch your rockets straight up to the Mun or Minmus. You have to aim, and time it well, and have a more powerful booster stage (you want to be going at least 1600 m/s before you switch to your upper stage) -- but it saves almost 50% on your travel time, and maybe 30% on the cost of your rocket, and it works with much more noodley rockets that would crash if you try to gravity turn them.

There are plenty of things that have to end up in LKO, of course. It's not like you will never go there. So this rule of thumb only applies when you have a choice.

-- And as far as sandbox goes: I kinda think it's always beneficial to have one of each going at the same time. The career mode game gives you odd targets to strive for, that you might never consider in sandbox mode. Once you have something you want to accomplish that you've never done before, you switch to the sandbox mode game and try 80 different ways to see if you can accomplish it. Or you need to design a ship to do a task, and you need to figure out how much fuel and how to steer and all the other design aspects of it -- so you try a dozen different designs in sandbox mode, and launch them, and see what they can do. Which also is very helpful when you forget stuff -- like landing legs or solar panels or antennas or science devices or ....

 

Thanks. I will try some of these tactics. I'm asking because I've been playing around with pre-made rockets in sandbox mode. Some of these rockets are described as having the ability to go to Minmus (at least i think) and I find a way to use up all of the liquid fuel just to get up to 170,000 m. I know, it's funny. Bear in mind, I've made it past the most basic of tutorials all with target assist on launch.

Edited July 31, 2016 by Buckeye1

[Red Iron Crown]

I would not do transfers to the moons without going to LKO first. While it is technically possible to do so for less delta-V and possibly cost, in practice it is quite difficult to do so, especially as a new player. It certainly won't save "50% of travel time and maybe 30% of the cost of the rocket".

[Reactordrone]

3 hours ago, Red Iron Crown said:

I would not do transfers to the moons without going to LKO first. While it is technically possible to do so for less delta-V and possibly cost, in practice it is quite difficult to do so, especially as a new player. It certainly won't save "50% of travel time and maybe 30% of the cost of the rocket".

I agree. In order to shoot straight up to the Mun you need  a higher thrust to weight ratio in your upper stages and that leads to extra weight and lower delta-v. As an extreme example I made a small probe for a recent challenge which is quite capable of landing on the Mun or Minmus by getting into orbit first but if you launch it straight upwards it will run out of fuel at about 300km altitude.

[bewing]

3 hours ago, Red Iron Crown said:

I would not do transfers to the moons without going to LKO first. While it is technically possible to do so for less delta-V and possibly cost, in practice it is quite difficult to do so, especially as a new player. It certainly won't save "50% of travel time and maybe 30% of the cost of the rocket".

Heh. I disagree. Adding a few kickbacks and launching straight up is ever so much simpler than nailing a perfect gravity turn. The only trick is getting the timing right, which is just a matter of doing one simulated launch, first. And the timing window is very wide.

Edited August 1, 2016 by bewing

[Red Iron Crown]

Just now, bewing said:

Heh. I disagree. Adding a few kickbacks and launching straight up is ever so much simpler than nailing a perfect gravity turn. The only trick is getting the timing right, which is just a matter of doing one simulated launch, first.

Kickbacks work just fine for putting stuff in orbit, too, and the gravity turn doesn't need to be perfect. Whereas the timing of a direct launch has to be awfully close to perfect, especially for Minmus or a satellite contract.

I'd contest "one test lauch" for that matter. Are you saying you can easily tell from the first test launch's trajectory how much time you must warp to get it right on the next launch? Or do you take a guess and possibly have to revert a second time? And how do you handle Minmus' inclination, since a direct launch only works easily every 25 days or so?

I consider getting to LKO one of the core skills of the game, and it's a good stepping stone to everything else for a variety of reasons.

[bewing]

4 minutes ago, Red Iron Crown said:

Kickbacks work just fine for putting stuff in orbit, too, and the gravity turn doesn't need to be perfect.

After adding a few kickbacks to a typical rocket's first stage, I tend to find the TWR is high enough (a bit over 2) that gravity doesn't turn you by itself. If you try to force it by steering, the rocket often goes unstable.

4 minutes ago, Red Iron Crown said:

Whereas the timing of a direct launch has to be awfully close to perfect, especially for Minmus or a satellite contract.

Nah. If you launch vertically, you are moving extremely slowly by the time you get to your Ap. You can spend days at the Ap, moving almost nowhere. This gives Minmus lots and lots of time to catch up to you, at a reasonable clip.

For a satellite contract you make minor adjustments after launch until your Ap touches the target orbit. Then burn at the Ap in the proper direction to set your inclination and Pe.

4 minutes ago, Red Iron Crown said:

I'd contest "one test launch" for that matter. Are you saying you can easily tell from the first test launch's trajectory how much time you must warp to get it right on the next launch?

Well, no. I meant one test launch ever. It's not the trajectory that matters (straight up and straight down to a well-defined height makes the trajectory pretty obvious) -- it's how much your target moon moves while you are getting there. The Mun moves 45 degrees. Minmus moves 30 degrees. Then you adjust the map so that your target moon is about that angle off vertical, and you launch when KSC gets to vertical. Works every time.

4 minutes ago, Red Iron Crown said:

And how do you handle Minmus' inclination, since a direct launch only works easily every 25 days or so?

A two or three second thrust north or south lines you up, once you are on your way.

4 minutes ago, Red Iron Crown said:

I consider getting to LKO one of the core skills of the game, and it's a good stepping stone to everything else for a variety of reasons.

Getting to LKO instead is helpful when you don't have enough thrust to do a successful vertical launch. But if you are at Minmus, and fully refueled, and a tug pushes you for 270 m/s back into a Kerbin orbit with a Pe at 75km -- that's always better than being in LKO from an Oberth perspective, just so long as the orbit is pointing in the right direction. So Minmus makes a better stepping stone than LKO.

 

[Spricigo]

 

1 hour ago, bewing said:

Heh. I disagree. Adding a few kickbacks and launching straight up is ever so much simpler than nailing a perfect gravity turn. 

Debug Menu and tick infinite fuel is even so much simpler than nailing a perfect proper design. 

[Red Iron Crown]

37 minutes ago, bewing said:

After adding a few kickbacks to a typical rocket's first stage, I tend to find the TWR is high enough (a bit over 2) that gravity doesn't turn you by itself. If you try to force it by steering, the rocket often goes unstable.

TWR of 2 on the pad is a bit high for mass efficiency. It's cheaper to go to space with an initial TWR of about 1.3-1.5, whether you want to go to LKO or beyond. Even if you want to do a direct ascent, it's still better to get the rocket turned on its side, as gravity losses are a thing.

37 minutes ago, bewing said:

Nah. If you launch vertically, you are moving extremely slowly by the time you get to your Ap. You can spend days at the Ap, moving almost nowhere. This gives Minmus lots and lots of time to catch up to you, at a reasonable clip.

Maybe, maybe not. You don't get the same ease of adjustment that one would get from LKO using maneuver nodes.

37 minutes ago, bewing said:

For a satellite contract you make minor adjustments after launch until your Ap touches the target orbit. Then burn at the Ap in the proper direction to set your inclination and Pe.

Well, no. I meant one test launch ever. It's not the trajectory that matters (straight up and straight down to a well-defined height makes the trajectory pretty obvious) -- it's how much your target moon moves while you are getting there. The Mun moves 45 degrees. Minmus moves 30 degrees. Then you adjust the map so that your target moon is about that angle off vertical, and you launch when KSC gets to vertical. Works every time.

All this is imprecise guesswork, though. We have good tools for planning orbital burns that makes such things unnecessary, why not avail of them?

37 minutes ago, bewing said:

A two or three second thrust north or south lines you up, once you are on your way.

 More guesswork, combined with steering losses.

37 minutes ago, bewing said:

Getting to LKO instead is helpful when you don't have enough thrust to do a successful vertical launch. But if you are at Minmus, and fully refueled, and a tug pushes you for 270 m/s back into a Kerbin orbit with a Pe at 75km -- that's always better than being in LKO from an Oberth perspective, just so long as the orbit is pointing in the right direction. So Minmus makes a better stepping stone than LKO.

We're slipping a bit away from the OP's "How do I get to space" question, but even using Minmus ISRU you're better off doing interplanetary from LKO. Back when I was using ISRU in the Kerbin system, I arrived at the following as the method to minimize fuel brought up from Kerbin:

1. Design the IP stuff so that the first 900m/s of Kerbin ejection burn is unfueled.
2. Launch the IP thing to LKO, using the IP fuel to help with orbital insertion.
3. Bring a tanker down from Minmus and rendezvous/dock with the IP craft.
4. Have the tanker + IP ship burn up to Minmus-altitude Ap.
5. Top off the IP ship and separate it.
6. Complete IP burn.
7. Wait for an encounter with Minmus for the tanker (no time pressure, not trying to hit a window).
8. Fill up tanker and repeat.

This technique puts the IP craft in the same fuel state as your scenario does, but has the benefit of being able to hit transfer windows precisely and using less fuel that I had to pay for.

[bewing]

33 minutes ago, Red Iron Crown said:

All this is imprecise guesswork, though. We have good tools for planning orbital burns that makes such things unnecessary, why not avail of them?

Because the tools are also unnecessary if you can do it all in a few seconds by eye. It just depends on how you look at it.

But the point of all this, to get back to the point I was making in my first post (on topic): is that there are several ways of doing all of this, and they all work fairly well, and you don't have to lock yourself into any one of them.

[Superfluous J]

9 hours ago, Buckeye1 said:

Is the thrust-to-weight ratio displayed in-game?

Not directly, but you can tell what it is (roughly) based on the G meter. If your G meter is 2 at full throttle, your TWR is (about) 2. If it's halfway between 1 and 2, it's (about) 1.5. Yes, this is also true while heading straight up.

Note this doesn't work for local TWR (or more precisely, it only works for local TWR at sea level on Kerbin) but it's "good enough" for many many purposes.

[Buckeye1]

7 hours ago, Red Iron Crown said:

I would not do transfers to the moons without going to LKO first. While it is technically possible to do so for less delta-V and possibly cost, in practice it is quite difficult to do so, especially as a new player. It certainly won't save "50% of travel time and maybe 30% of the cost of the rocket".

When you say LKO are you implying I use a gravity turn to get there? I was playing around in career and built a rocket with level 3 parts that was capable of reaching ~94,000 m. I pretty much went up vertically and I did not have enough fuel to create a full orbit. But I suspect that if I tried angling it, my rocket would have cart-wheeled. I guess this is the challenge of the game. One of my issues is that I don't know how far a certain amount of fuel will take me under the ideal scenario. Let's say I was able to get 4 FLT100's into Kerbin's upper atmosphere with a nice gravity turn to top it off. Can I expect that to create an orbit that doesn't have a periapsis in the center of Kerbin?

[Reactordrone]

47 minutes ago, Buckeye1 said:

When you say LKO are you implying I use a gravity turn to get there? I was playing around in career and built a rocket with level 3 parts that was capable of reaching ~94,000 m. I pretty much went up vertically and I did not have enough fuel to create a full orbit. But I suspect that if I tried angling it, my rocket would have cart-wheeled. I guess this is the challenge of the game. One of my issues is that I don't know how far a certain amount of fuel will take me under the ideal scenario. Let's say I was able to get 4 FLT100's into Kerbin's upper atmosphere with a nice gravity turn to top it off. Can I expect that to create an orbit that doesn't have a periapsis in the center of Kerbin?

A gravity turn (or an approximation of one) is the usual method of getting into orbit and getting into orbit is the usual first step to going anywhere. Orbiting is all about going horizontally at high speed and the gravity turn gives a good, gradual change from going up (to get out of the thicker parts of the atmosphere) to going horizontally and when done well it doesn't require any control inputs after the initial push over.

To know how far your fuel will get you you'll need to know the delta-v of the ship and the required delta-v of the trip. There are plenty of delta-v maps out there that will give you an idea of how much delta-v you'll have to pack and for working out what your ship's delta-v is you'll need the Tsiolkovsky rocket equation, there are mods out there that will calculate it for you or you can do it yourself fairly easily.

The other option, of course, is trial and error and the sandbox is a good place to test designs and you can pretty much get anywhere in KSP by just playing and learning from failure (or successes )

[bewing]

4 hours ago, Buckeye1 said:

When you say LKO are you implying I use a gravity turn to get there? I was playing around in career and built a rocket with level 3 parts that was capable of reaching ~94,000 m. I pretty much went up vertically and I did not have enough fuel to create a full orbit. But I suspect that if I tried angling it, my rocket would have cart-wheeled. I guess this is the challenge of the game. One of my issues is that I don't know how far a certain amount of fuel will take me under the ideal scenario. Let's say I was able to get 4 FLT100's into Kerbin's upper atmosphere with a nice gravity turn to top it off. Can I expect that to create an orbit that doesn't have a periapsis in the center of Kerbin?

They way I figured it when I was starting out (after some testing and failing) was that with the typical engines, aerodynamic control, etc., etc., that I had at the beginning of the game, I needed about 400 units of liquid fuel in my upper stage to get into an actual orbit.

[foamyesque]

Even if you're doing a direct ascent, without a stop in an LKO parking orbit -- which I've done on occasion, though not often -- it's by no means more efficient to go straight up. Simpler, maybe; more efficient, no. Gravity losses are a thing, as said above; trying to minimize them through turbocharged TWR is a mug's game, since it wrecks your mass ratio and (on Kerbin or Eve) risks thermal issues. Going lateral is just better.

 

If you're not able to turn with your solids on, you're building your rocket wrong.